Proteins and other large bioloqical molecules, including DNA, may be separated for analysis using electrophoresis techniques. One particularly important application of these techniques is the sequencinq of the DNA and RNA molecules. In performinq an electrophoresis separation of such molecules, a gel is formed between two non-conducting plates, such as glass, to form a thin sheet of gel between the glass surfaces.
The collection of molecules to be sorted is placed at the negative electrode end of the gel, usually in pre-formed wells. The molecules are negatively charqed, and the electric field in the qel reacts with the charge on the molecules to provide a force propelling the molecules through the gel towards the positive electrode. Smaller molecules have less resistance to traveling through the gel than larger molecules, resulting in a separation and sorting of the molecules by size as they migrate throuqh the gel.
Synthesis of fractional lengths of DNA (or RNA) molecules by means of enzymes allows the molecule to be analyzed according to the sequence of bases making up such a molecule. Techniques for doing this type of analysis are well known. See for example Sanger. F., S. Nicklen & A.R. Coulson 1977 Proc. Natl. Acad. Sci. USA 74: 5463-5467; Prescott L. Deininger Analytical Biochemistry 135, 247-263 (1983); Garoff, H., & Ansorge, W. (1981) Anal. Biochem. 115, 450-457; and Biggin, M. D., T. J. Gibson & A. F. Hong 1983 Proc. Natl. Acad. Sci. USA 80: 3963-3965.
It is important to the proper functioning of the electrophoresis process that the gel be uniform in thickness and other property in the region where the separation is performed. Non-uniformities in the thickness of the gel result in perturbations of the electric field which will adversely affect the accuracy of the electrophoresis separation. The present invention is directed toward maintaining uniform qel thickness in an electrophoresis cassette.